VATN Displays

Anyone tried these VATN LCD displays? Apparently, they offer much better contrast than standard LCD character displays, but I’ve never seen one in action.

I have a couple of Shruthi-1 main boards to make up, so might try one myself.

a|x

Apparently you need this :

So rather than connect pin 15 to ground, you use it as the negative input to the contrast trimmer, so you can vary Vo between Vee and Vdd.

I think the display must have a build in inverter to produce the negative voltage required. So you need to disconnect the GND pin of the contrast trimmer and connect it to pin 15 directly instead.

Given where the GND PCB trace is this won’t be easy as cutting the trace by the trimmer will break the GND trace. It would be easier to disconnect pin 15 from GND by cutting the trace near pin 15 on the LCD connector, then wire a pot which you would mount in the case.

Do you have a link?

Oh, sorry, I intended to include a link.
Try here

a|x

Very interesting! Thanks for sharing this nice finding.
It’s not 100% compatible though:

  • the backlight is powered by Vdd pin 2 (and not pin 15) and pin 16

  • pin 15 provides a negative voltage which you probably need for driving the LCD contrast setting
    (connect this pin to the contrast trimmer instead of the trimmers GND)

But this should be no real problem with some modification.

I’d assumed the pinout was the same as the standard LCDs.

a|x

Looks perfectly fine to me, except for Vee?

Why is pin 15 an output not an input, see the VOP diagram here in comparison:

http://www.rapidonline.com/pdf/57-2232.pdf

Pin 15 is normally (not on this display) the backlight power supply. Pin 16 is GND.
See my post above!
To disconnect pin 15 from the display, you just don’t need to put the backlight resistor in. Or just clip the corresponding header pin.

@cj55 or just remove it from the strip, by pulling hard on it.

I would love to see a comparison of these vs. “traditional” negative displays. I’m having a hard time understanding the difference - they’re both black background without backlight bleeding trough… And the price seems comparable.
Hrmm… That reminds me, I’ve got a negative red display ready for my Shruthi-1 Polivoks waiting for me to get the parts & assemble the digital board… :slight_smile:

@V’cent I’ve yet to see a negative LCD with anything like a black background. They always look black in the product shots, but the reality is always quite different, in my experience. The VATN displays are supposed to be much nearer to OLEDs (i.e. with a genuinely dark background), but, hopefully, without the noise problems they tend to cause.

a|x

Hmm, that does sound pretty good…

In case anyone gets one of these, can you please, please post an image here?

Don’t know if all the OLEDs cause noise though. The Winstar OLEDs I got from Rapid have been behaving nicely, but I did put some smoothing caps on their power lines.

Guess I hafta try one of the VATN displays too. Wonder where I can put that? Maybe some old Casio CZ?

Well if they’re using some sort of voltage inverter like an OLED might, then I’d expect that may cause noise?

Depends on the inverter, but it is a risk for sure. The testing is the pudding, or something.

I like pudding… :stuck_out_tongue:

a|x

Perhaps we need an LCD noise tester PCB.